This invention relates to a magnetic pole material for a magnetic head, a composite thin film magnetic head using the same, and a magnetic memory device comprising the composite thin film magnetic head.
In order to realize high-density recording, a magnetic head mounted on a magnetic memory device is required to generate a recording magnetic field more and more increased in magnetic field strength.
In recent magnetic memories such as a magnetic disk unit, a composite thin film magnetic head is predominantly used as a recording/reproducing device. The composite thin film magnetic head comprises a magnetoresistive head and an inductive head as a reproducing head and a recording head, respectively. By individually optimizing the reproducing head and the recording head, the magnetic memory device can further be improved in performance.
In order to increase the magnetic field strength of the recording magnetic field, it is necessary to use a magnetic pole material having a high saturation flux density as a magnetic pole layer of the inductance head. Furthermore, it is essential that the magnetic pole material is easily magnetized under a magnetic field generated by a coil. Therefore, the magnetic pole material must be a magnetic material small in coercive force and high in permeability, i.e., an excellent soft magnetic material.
As the magnetic pole material of the inductive head, use has widely been made of a Nixe2x80x94Fe alloy (permalloy) produced by electroplating.
In the above-mentioned composite thin film magnetic head, use is often made of a permalloy which has a composition range such that the content of Ni is on the order of 81-82 wt % and which has a magnetostrictive constant approximately equal to zero. The permalloy having the above-mentioned composition range will hereinafter be referred to as a 82 permalloy. The 82 permalloy has a saturation flux density between 9000 and 10000 G (gauss). If an excellent soft magnetic material having a higher saturation flux density is used, it is possible to produce a magnetic head having a recording magnetic field great in magnetic field strength and steep in magnetic field gradient.
To this end, proposal has been made of various materials as a soft magnetic material which is for use in a magnetic head and which has a saturation flux density higher than that of the 82 permalloy. In particular, a Coxe2x80x94Fexe2x80x94Ni magnetic film made of a Coxe2x80x94Fexe2x80x94Ni ternary alloy is small in coercive force and magnetostrictive constant and has a high saturation flux density not smaller than 14000G. Therefore, extensive consideration has been made of the composition of the Coxe2x80x94Fexe2x80x94Ni alloy and an additive thereto.
For example, Japanese Unexamined Patent Publication (JP-A) No. H05-263170 discloses a thin film magnetic head using a Coxe2x80x94Fexe2x80x94Ni film containing 60-90 wt % Co, 3-9 wt % Fe, and 5-15 wt % Ni.
Japanese Unexamined Patent Publication (JP-A) No. H08-241503 discloses a thin film magnetic head using a Coxe2x80x94Fexe2x80x94Ni film containing 60-80 wt % Co, 8-25 wt % Fe, and 15-25 wt % Ni.
Japanese Unexamined Patent Publication (JP-A) No. H08-321010 discloses a thin film magnetic head using a Coxe2x80x94Fexe2x80x94Ni film containing 60-75 wt % Co, 3-9 wt % Fe, and 17-25 wt % Ni.
However, each of the above-mentioned Coxe2x80x94Fexe2x80x94Ni films produced by conventional methods has a saturation flux density on the order between 14000 and 18000 G and does not achieve a saturation flux density of a yet higher level. In addition, because of inclusion of such a large content of Co, each of the Coxe2x80x94Fexe2x80x94Ni films is inferior in corrosion resistance than a permalloy film. The corrosion resistance is required to assure the reliability of a device such as a magnetic head in which the Coxe2x80x94Fexe2x80x94Ni film is used.
Japanese Unexamined Patent Publication (JP-A) No. H11-74122 discloses a Coxe2x80x94Fexe2x80x94Ni film containing 40-70 wt % Co, 20-40 wt % Fe, and 10-20 wt % Ni and a method of producing the same. The Coxe2x80x94Fexe2x80x94Ni film disclosed in this publication has a high saturation flux density on the order between 19000 and 22000 G and a low coercive force not greater than 2.5 Oe.
However, the increase in magnetic recording density requires a magnetic head having a higher recording ability. Following the recent progress in increase of the magnetic recording density, a minimum magnetic reversal area as a recording unit becomes so small and is therefore susceptible to the influence of thermal energy even at the room temperature. At a recording density exceeding 10 gigabit/in2, recording magnetization becomes unstable due to thermal fluctuation.
In order to minimize the thermal fluctuation, it is most effective to enhance anisotropy energy of a magnetic layer of a magnetic recording medium so as to stabilize the recording magnetization against the thermal fluctuation. However, such enhancement of the anisotropy energy is equivalent to an increase in strength of a magnetic field required to reverse the magnetization, i.e., an increase in coercive force of the magnetic recording medium. In order to write data into the magnetic recording medium having a large coercive force, it is necessary to increase the strength of a recording magnetic field of the magnetic head. Therefore, a magnetic material having a high saturation flux density and capable of generating a stronger recording magnetic field is required to meet further increase in magnetic recording density.
It is an object of this invention to provide a soft magnetic film small in coercive force and magnetostrictive constant and having a high saturation flux density on the order between 20000 and 23000 G.
It is a specific object of this invention to provide a magnetic material having a less Ni content to achieve a greater saturation flux density with a coercive force and a magnetostrictive constant kept sufficiently small.
It is another object of this invention to provide a magnetic head comprising the above-mentioned magnetic film.
It is still another object of this invention to provide a magnetic memory device capable of suppressing thermal fluctuation even at a high recording density by combining the above-mentioned magnetic head and a recording medium having a large coercive force.
According to this invention, there is provided a CoxFeyNiz magnetic film having a composition represented by a chemical formula of CoxFeyNiz (50xe2x89xa6xxe2x89xa680, 20xe2x89xa6yxe2x89xa640, and 3xe2x89xa6z less than 10 (wt %)) and having an average grain size not greater than 40 nm.
The above-mentioned magnetic film contains a large amount of Co. However, it is possible to improve an corrosion resistance of the film if the content of S (sulfur) as an impurity contained in the film is not greater than 0.1 wt %.
According to this invention, there is also provided a composite thin film magnetic head comprising a reproducing head and an inductive head. The inductive head has a magnetic pole layer a whole or a part of which comprises the above-mentioned Coxe2x80x94Fexe2x80x94Ni magnetic film. In this case, the Coxe2x80x94Fexe2x80x94Ni magnetic film preferably has a thickness between 0.3 and 2.0 xcexcm (both inclusive).
According to this invention, there is also provided a magnetic memory device comprising a combination of the above-mentioned composite thin film magnetic head and a magnetic recording medium. In this case, the magnetic recording medium preferably has a coercive force not smaller than 3500 Oe. If the magnetic recording medium has a greater coercive force not smaller than 5000 Oe and a yet greater coercive force not smaller than 7000 Oe, the magnetic memory device is less susceptible to the influence of thermal fluctuation even upon high-density recording.